An optical phenomenon is any observable event which results from the interaction of light and matter. See also list of optical topics and optics
Common optical phenomenon are often due to the interaction of light from the sun or moon with the atmosphere, clouds, water, or dust and other particulates. One common example would be the rainbow, when light from the sun is reflected off water droplets in rain as it falls to the ground. Others, such as the green ray, are so rare that many consider them to be mythical. Some, such as instances of fata Morgana, are commonplace only in certain locations.
Other phenomena are simply interesting aspects of optics, or optical effects. The colors generated by a prism are often shown in classrooms for instance.
Some optical illusions can be explained as observations of unusual optical phenomena.
Atmospheric optical phenomena include:
- Alexander's band, the dark region between the two bows of a double rainbow.
- Auroral light (northern and southern lights, aurora borealis and aurora australis)
- Elves 
- the Green ray
- Halos, of Sun or Moon
- Sprites 
- Sun dogs
- Asterism, star gems such as star sapphire or star ruby.
- Aventurescence, spangled gems such as aventurine quartz and sunstone.
- The Camera obscura
- Chatoyancy, cat's eye gems such as chrysoberyl cat's eye or aquamarine cat's eye
- Chromatic polarization
- Diffraction, the apparent bending and spreading of light waves when they meet an obstruction.
- Double refraction
- The Double-slit experiment
- fluorescence, also called luminescence or photoluminescence.
- metamerism as of alexandrite
- pleochroism gems or crystals which seem many-colored
- Rayleigh scattering (Why the sky is blue, sunsets are red, clouds are white, and associated phenomena)
- Synchrotron radiation
- The separation of light into colors by a prism
- The Zeeman effect
- Thomson scattering
- Total internal reflection
- The Umov effect
- Polarized light-related phenomena such as double refraction, or Haidinger's brush
- The ability of light to travel through space or through a vacuum.
- The unusually large size and rich color of the Moon as it rises and sets
Observations of some phenomena such as the photoelectric effect, the flow of electric current in a material or through a vacuum (as in a photocell) when the material is exposed to light, led to advances in science, as they could not be easily explained by existing theory.